1. Field of the Invention
The present invention is directed to a linear oscillating actuator, and more particularly to a linear oscillating actuator having a pair of oscillators moving in parallel paths for driving individual loads.
2. Description of the Prior Art
A linear oscillating actuator has been utilized in many fields as an alternative to the rotary driving source. Particularly, as disclosed in U.S. Pat. No. 5,632,087, the linear actuator has found itself advantageous for use as a driving source of dry shavers of reciprocatory type. When applied to the shaver having a pair of inner cutters, i.e., the reciprocating loads, the linear oscillating actuator is designed to have a corresponding pair of oscillators running in parallel oscillating paths and being adapted for driving connection respectively with the inner cutters. In this instance, each individual oscillating system composed of the oscillator and the corresponding reciprocating load has its mass center offset in a lateral direction perpendicular to the oscillating direction from a mass center of the actuator or the shaver. Due to this offset arrangement of the individual oscillating systems from the mass center of the actuator, the actuator suffers from undesired vibrations around its mass center
The present invention has been achieved in view of the above problem to provide an improved linear oscillating actuator which is capable of minimizing the undesired vibrations, while moving a pair of oscillators in parallel paths. The linear oscillating actuator in accordance with the present invention includes a stator having one of an electromagnet and a permanent magnet, first and second oscillators each having the other of the electromagnet and the permanent magnet, and a chassis fixedly mounting the stator and movably supporting the first and second oscillators in such a manner as to allow them to move respectively in parallel linear paths. The electromagnet includes a winding receiving a drive current to generate a magnetic field which interacts with the permanent magnet to cause the oscillators to oscillate relative to the stator respectively in the parallel linear paths. A first drive element integrally projects from the first oscillator and is adapted to be connected to a reciprocating load for driving the same, while the second drive element integrally projects from the second oscillator and is adapted to be connected to a reciprocating load for driving the same. An important feature of the present invention resides in that the first and second drive elements project upwardly respectively from the first and second oscillators such that the first drive element is disposed immediately upwardly of the second oscillator and the second drive elements is disposed immediately upwardly of the first oscillator. With this reverse arrangement of the first and second drive elements relative to the first and second oscillators, the individual oscillating systems each including the oscillator, the drive element and the corresponding reciprocating load can have its mass center disposed in close proximity to a mass center of the actuator, thereby enabling to reduce undesired vibrations which would otherwise occur around the mass center of the actuator.
The first and second oscillators are configured to have lengths respectively extending along the liner paths and to have respective upright axes. In a preferred embodiment, the first drive element is integrally connected to a lengthwise center of the first oscillator by way of a center stem which extends obliquely with respect to the upright axis of the first oscillator, while the second drive element is integrally connected to opposite lengthwise ends of the second oscillator by way of a gate which is offset laterally in a direction perpendicular to the length of the second oscillator. The gate has an opening through which the center stem of the first oscillator extends loosely so that the first drive element is allowed to oscillate without being jammed with the second drive element. Thus, the first and second drive elements can be successfully disposed respectively immediately above the second and first oscillators without sacrificing the oscillatory movement.
Projecting on top of the first oscillator is a reinforcement fin which merges into the juncture of the center stem with the first oscillator. The reinforcement fin extends in the lengthwise direction of the first oscillator over a distance greater than the lengthwise dimension of the center stem measured with respect to the length of the first oscillator. With the inclusion of the reinforcement fin, the first oscillator is given sufficient rigidity against deforming force acting in the lengthwise direction along the oscillating path, assuring a stable and reliable oscillating performance.
The gate on the side of the second oscillator is shaped to have a bridge anchored at its opposite ends to the lengthwise ends on top of the second oscillator so as to define the opening between the bridge and the second oscillator. The reinforcement fin opposes the bridge with a small clearance therebetween so as to be capable of bearing the bridge when the second drive element is depressed. Thus, the gate can be protected against a possible impact or stress applied to the reciprocating load or the second drive element.
Further, the bridge may be formed at its longitudinal center with a raised platform from which the second drive element projects in order to strengthen the joint between the second drive element and the second oscillator sufficiently to withstand the impact or stress applied to the second drive element.
The first and second oscillators have respective legs for anchored connection with the chassis. Further included in the actuator is a link which interlocks the first and second oscillators in such a manner as to oscillate the oscillators in opposite phase. In this connection the leg of each of the first and second oscillators is connected to the link at a point below the anchored connection of the leg with the chassis. That is, each oscillator is connected to the chassis and also to the link at vertically spaced points, thereby requiring no extra dimensions with respect to the longitudinal and lateral directions for the interlocking connection, and therefore contributing to a compact design.
The center stem of the first oscillator can be given increased rigidity by a reinforcement member embedded therein. The reinforcement member may be either in the form of a metal pin or a part of a back yoke provided in the first oscillator adjacent to the permanent magnet. The metal pin may project out of the first drive element for driving connection with the reciprocating load.
The first and second oscillators are suspended frown the chassis by means of respective leaf springs so that the oscillators are movable only along the linear oscillating paths under the bias of the springs. Each leaf spring has a portion wider than a thickness of a corresponding one of the first and second oscillators so as to be given sufficient resistance to a torsion for stably supporting the oscillator. The leaf spring is offset laterally relative to the corresponding ones of the first and second oscillators in the thickness direction thereof, while being disposed close to each other in the thickness direction. Thus, the first and second oscillators can be held close to each other, yet allowing the use of the leaf springs having the wider portion than the thickness of the oscillator. Whereby, it is possible to make compact the actuator in the thickness direction of the oscillators while stably supporting the oscillators to the chassis.
In a preferred embodiment, the leaf spring is connected at its upper end with the chassis and at its lower end with one of the first and second oscillators. The lower end of the leaf spring may be configured to have a width either substantially equal to or less than that of the upper end of the leaf spring.
Further, in order to facilitate the connection of the leaf spring to the oscillator, the leaf spring may carry at its lower end a joint which is molded from a plastic material to have a means for connection with the corresponding one of the first and second oscillators. In this connection, the leaf spring may be formed with a hole into which a portion of the joint engages for firmly securing the joint to the leaf spring. The joint has a projection for insertion into a recess formed in the lower end of the corresponding one of the first and second oscillators.
The present invention further discloses a unique structure of mounting the stator to the chassis. The stator has the electromagnet composed of a core and the winding disposed around the core. The core has an upper end which opposes the permanent magnet on the side of the first and second oscillators to define therebetween a magnetic gap. The core is formed at its lower end with an extension having a stator""s mating surface which abuts against a chassis""s mating surface at a corresponding portion of the chassis for welding connection of the stator with the chassis. Preferably, both of the stator""s mating surfaces and the chassis""s mating surface are finished as flat horizontal surfaces.
The extension may also include a first stopper which engages with the chassis to fix the stator thereto with respect to a longitudinal direction along the linear path, and a second stopper which engages with the chassis to fix the stator thereto with respect to a lateral direction perpendicular to the longitudinal direction. Thus, the stator can be positioned accurately relative to the chassis without requiring external jig.
Further, the core may be given a means for latching engagement with a coil bobbin interposed between the core and the winding for stably holding the coil bobbin in position.